9. Phospholipid bilayer forming cell surface Receptor (blue) with bound ligand (purple) Receptor (green) with bound ligand (yellow) While this image actually shows something else, it gives a good impression of how receptors are found on the cell surface, and how they interact with ligands. In our case, the ligands would be attached to the macrophage cell surface in much the same way as the receptors are shown here. Our macrophage in this game will be shown with an attachment ligand on its surface, and the endothelia will have many different types of receptor. The player will have to find and match the proper receptor and ligand pair to get binding and to slow down. Cell interior